Lay Description: Wound healing in the cornea is incompletely understood;yet each year thousands of people elect corrective photorefractive surgery. Identification of mechanisms involved in wound healing will lead to the development of treatments for patients who do not heal properly. In this proposal, thrombin, a protease that generates fibrin and regulates cellular processes, will be studied. Scientific Description: The goal of this application is to test the hypothesis that thrombin is involved in corneal wound healing through cleavage of protease activated receptors and initiation of signaling pathways. Our preliminary data show the components required to convert prothrombin to thrombin and protease activated receptors mRNA in the human cornea and the ability of thrombin to alter corneal stromal cell gene expression and cell division. The thrombin inhibitor hirudin inhibits corneal epithelial wound healing. The SPECIFIC AIMS of this proposal are: 1) TO DETERMINE WHETHER THROMBIN CAN REGULATE KNOWN CELLULAR STEPS IN CORNEAL WOUND HEALING. Cultured corneal epithelial cells, stromal keratocytes,fibroblasts and/or myofibroblasts treated with thrombin will be assayed for thrombin dependent changes in phenotype, apoptosis, total cell number, cell division, and migration. 2) TO DETERMINE WHETHER THROMBIN STIMULATES CORNEAL STROMAL CELL SYNTHESIS OF PROTEINS INVOLVED IN WOUND HEALING. The effect of thrombin on cytokine, chemokine, growth factor and plasminogen activator system component synthesis will be determined using real-time RT-PCR to characterize thrombin dependent mRNA changes and ELISA and/or western blots for changes in protein levels. 3) TO DETERMINE THE MECHANISM OF INDUCTION OF THROMBIN EFFECTS ON CORNEAL CELL FUNCTION AND GENE EXPRESSION. The mechanism of thrombin induced changes in cell division of stromal myofibroblasts and stimulation of PAI-1 synthesis will be determined using thrombin inhibitors, inactivated thrombin, thrombin peptides, agonist and antagonists to thrombin sensitive protease activated receptors and signaling pathway inhibitors. 4) TO DETERMINE WHETHER THROMBIN AND PAR-1 ARE IMPORTANT FOR CORNEAL WOUND HEALING IN VIVO AND IN ORGAN CULTURE. Rabbit and human organ culture models and an in vivo model using normal and PAR-1 deficient mice will be used for these studies.